The young eye has the capability of focusing far and near objects, a capacity known as accommodation. The human crystalline lens, the second of the lenses, behind the cornea, which forms the eye optical system, responds to an accommodative stimulus by changing its shape in order to change its dioptric power. The ciliary muscle transmits a primarily equatorial force through its zonular fibers to the capsular bag (the outer membrane of the crystalline lens). When the crystalline lens is disaccommodated, the ciliary muscle relaxes, stretching the zonular fibres which in turn stretch the capsular bag, and flatten the surfaces of the crystalline lens. When the crystalline lens is accommodated, the ciliary muscle contracts relaxing the zonular fibers, thereby allowing the capsular bag to adopt a more curved shape. With aging the crystalline lens progressively loses elasticity and thus a loss of the accommodating capacity (a condition known as presbyopia). At a more advanced stage of aging, the crystalline lens moreover loses transparency (a condition known as cataract) making necessary an exchange of the opacified crystalline lens by an artificial intraocular lens by means of cataract surgery.
In current cataract surgery, a window is made in the capsular bag (capsulorrhexis) either by mechanical means or, since more recently, with femtosecond laser. The content of the crystalline lens (previously fractured either by phacoemulsification or, since more recently, by laser) is extracted through the capsulorrhexis, by aspiration. The intraocular lens is implanted, generally folded, through a small corneal incision, into the capsular bag where it unfolds. Generally the intraocular lens is stabilized in the capsular bag by means of plates or curved prolongations, called haptics, which tighten the equatorial region of the capsular bag.
Today the more frequently implanted lenses are monofocal. Pseudophakic patients and presbyopic patients (who are implanted with monofocal intraocular lenses) only perceive one focus plane, which makes it necessary to resort to the use of near vision, bifocal or progressive spectacles (using an optical correction with a different power for each eye), or multifocal contact lenses to provide near vision. None of these solutions offers a satisfactory correction of presbyopia because the dynamic capacity of accommodation of the young eye is not restored.
During the last years a great number efforts have been invested in the replacement of the rigid or opacified crystalline lens by a filler material which may be a flexible polymer or a gel, with or without membrane coating, injected in the emptied capsular bag, as described for example in patent application WO2012/126053. This kind of approach to restore accommodation depends on the capsular integrity, its transparency as well as the stability of its mechanical properties. These attempts have been unsuccessful due to capsular fibrosis which usually occurs in the months following cataract surgery due to proliferation and transdifferentiation of the epithelial cells of the crystalline lens, and which results in a dramatic change of the mechanical properties of the capsular bag which loses both its elasticity and transparency. In contrast to what happens with conventional intraocular lenses where the capsule is not necessary for correct functioning of the intraocular lens, and transparency can thus be returned to the eye by making an opening in the opacified posterior capsular bag, which is usually done by laser (posterior laser capsulotomy), in the case of capsular bags provided with a filler material, capsular fibrosis has become an insurmountable obstacle where mechanical integrity is indispensable, this causing capsular refilling techniques, at least nowadays, to be clinically unviable.
Furthermore, in the last years numerous accommodating intraocular lenses have been proposed, which are provided with mechanisms that contrarily to monofocal intraocular lenses, with one fix focus plane, aim to dynamically alter the power of the eye. The majority of these designs have failed for not being based on a correct understanding of the accommodating mechanism, being dependent on the integrity of the capsular bag after surgery, not using the available accommodating forces, or limitations in the design of the operation of the intraocular accommodating lens.
Thus, at present, the only accommodating lens approved by the US Federal Drug Administration (CRYSTALENS, marketed by Bausch and Lomb, NY, USA) is a single optic intraocular lens, with haptics provided with a hinge (Cumming, US20040249456) which provide for a possible axial movement of the optic area of the intraocular lens and thus a change in ocular refraction. Although, nominally, the intraocular lens should move forward in the accommodated state, it has been proved that in many patients the optical lens actually moves backwards in response to an accommodative stimulus. Moreover, a relevant change in refraction would need a forward movement of 1 mm of the intraocular lens in the anterior segment of the eye, which is not achieved in any patient. Another intraocular lens (TETRAFLEX Lenstec, FL, USA) does not use hinges, but its principle is also based on axial displacement. Further, there is at least one accommodating intraocular lens in the market (SYNCHRONY, marketed by Advanced Medical Optics, CA, USA), and other accommodating intraocular lenses proposed in patents which are constituted by two joined lenses linked by some mechanism which transforms accommodating forces into a relative displacement of the two optics with respect to each other so as to provide a change in optical power. The majority of these lenses assume an axial displacement along the optical axis, although some assume a lateral movement based on the Alvarez principle (such as the AKKOLENS of Akkolens International, Netherlands).
One frequent problem identified in many of the proposals regarding accommodating lenses is the lack of connection between the capsular bag and the intraocular lens system which allow adequately transferring the movement of the ciliary muscle to the operating mechanism of the intraocular lens, as described in U.S. Pat. No. 7,150,760B2. Some lenses try to achieve the fastening means of the natural fibrosis occurring at the haptics during the weeks following implantation of the intraocular lens, as described in US2005/0119741A1. Several haptics' devices and designs have been proposed to favor said fibrosis process, as for example ring shaped collars as those proposed by Cummings (US2001/0005794A1); the so called zonular capture haptic which favors fusion of the capsular bag to the haptics using the natural fibrosis process (Beer, in US2011/0307058A1); a porous or perforated plate as a retaining structure for an accommodating lens (Glasser and Coleman, in US2008/0221676), or contact plates along the equatorial region (separating anterior and posterior capsule) with a relatively large contact surface to promote cell and fiber proliferation in the anchoring area of the intraocular lens to the capsular bag (Lang, in U.S. Pat. No. 6,660,035B1). Depending on the natural fibrosis in respect of the mechanism for connecting the intraocular lens and the capsular bag has several drawbacks, such as the duration of this process (weeks), the relative uncertainty of the symmetry, and the result of the final anchorage. Some authors have proposed mechanical anchorages of the intraocular lens to the edge of the capsulorrhexis using clasps, brackets or pins (Peng US2003/0204254A1) or bioadhesives (Reisin, US2011/0029074A1; Thomson WO1996/035398A1).
The human crystalline lens changes its shape while accommodating, so that an intraocular lens design based on the surface shape change would mimic the natural accommodating mechanism more closely in contrast to axially displacing lenses. Several patents propose multi-mechanism designs which simultaneously displace and deform (Paul, in US2004/0127984A1). Several proposals propose global general concepts of an intraocular lens, operating by one or two optics moving axially or by means of changes in curvature (Cumming, en US2008/0269887).
Several designs propose intraocular lenses conceived to change curvature in response to an accommodating force. However, several of these designs fail regarding the operation principle they are based on. For example the “Nulens” of the company (Nulens Ltd., Israel, consists of two plates separated by a viscoelastic material, the anterior one of which has an aperture. The mechanism of this intraocular lens assumes that the capsular bag (emptied from its crystalline content) exerts o force upon the posterior plate, which should become a piston approaching both plates in such a way that the elastic polymer bulges through the anterior aperture thus forming a more curved intraocular lens. It has been shown that, completely unlike the natural crystalline lens the greatest curvature is achieved in the disaccommodated condition. Other proposals consider hinge mechanisms comprising one or two deformable lenses, although they consider that the mechanism by which the intraocular lens increases its dioptric power, is based on an increase of the pressure in the vitreous cavity. (Cummings, in US2008/0269887A1). Other lenses (Woods, in U.S. Pat. No. 6,217,612B1) define an intraocular lens constituted of polymer material with a elastic memory, the concept of which is interesting inasmuch they would have the shape of maximum accommodation in the absence of zonular tension (as it happens in the young human eye). However, this intraocular lens depends critically on the general integrity of the capsular bag because the pressure exerted by the walls of the capsular bag upon the intraocular lens.
Other accommodating intraocular lenses proposing the modification of the dioptric power of the intraocular lens by a change of the curvature of its surfaces, are those based on fluids, generally covered by a membrane. In general, said lenses design have complex designs, as they require, among other elements, the presence of reservoirs, valves, systems for evacuation and circulation of the fluid. Besides, the principle of transmitting the forces of the ciliary muscle to these lenses is not always adequate. One of the first proposed fluidic lenses (Schachar, in U.S. Pat. No. 4,373,218A) suggests the use of electrodes and microprocessors to control the forces exerted upon the lens. Another document (Chawdhary, US2007/0129798A1) proposes a deformable fluidic device, generally in combination with a rigid intraocular lens implanted in the ciliary sulcus with the purpose of being in response to the forces of the ciliary muscle. The direct coupling of the lens to the ciliary muscle seems to be little viable in practice due to the textures and consistency of said tissue. One of the most advanced fluidic lenses is the one developed by Powervision, CA, which has already been implanted in patients. This is an intraocular lens with microchannels for fluid circulation and reservoirs placed in the haptics. One of the limitations of this intraocular lens is its dependency on the size of the capsular bag and the integrity thereof, for its functioning.
Regarding several lenses of a deformable type, the advantages of one fixed and one deformable have been highlighted. The fixed component would provide the correction of the refractive error of the patient while the deformable component would provide the dioptric change needed to accommodate at several distances. Turley (U.S. Pat. No. 4,892,543B1) proposed an intraocular lens with two components (of fixed and variable power respectively) emphasizing that the first optical component would still be working even if the second component failed or was destroyed providing a security feature to the intraocular lens. One limitation of this proposal is its implantation in contact with the ciliary muscle. Thomson (WO1996/035398A1) proposed an intraocular lens with a fixed component and another deformable one, with the deformable part connected to an anchoring system of the intraocular lens and to the capsular bag. However, said anchoring is limited to a mechanical or glued connection of only the border of the capsulorrhexis therefore wasting the forces applied directly equatorially to the capsular bag. Brady (US2007/0078515) proposed an accommodating intraocular lens with two components, one fixed and one deformable. In this case, the deformation occurred due to pressure and contact between the two components of the intraocular lens. In a later patent, Brady (U.S. Pat. No. 7,713,299B2) presents a haptic system for anchorage of the intraocular lens and the capsular bag adapted for accommodating intraocular lenses with two components: one deformable and one fixed. Weinschenck (U.S. Pat. No. 6,645,246B1) proposed an intraocular lens with two components, one fixed and one deformable; the rigid part constitutes the core of the accommodating intraocular lens and the flexible part is linked to the capsule by a rigid force transmission assembly.
However none of the proposed or available accommodating intraocular lenses provides the eye with the accommodating capacity of the young crystalline lens in an effective manner.